In recent years, there is widely used a display apparatus using a planar light source device (back light) for irradiating a light from a back face or a side face of a panel, such as a liquid crystal display. Conventionally, the main stream of such a back light illuminant for a liquid crystal display has been the so-called edge light type in which a cold cathode tube as an illuminant is disposed on the edge face of the chassis for thinning and low power consumption of the apparatus.
As such a back light illuminant of the edge light type, an illuminant with a configuration shown in FIG. 24 is used.
More specifically, for a back light illuminant 100 of the edge light type, a cold cathode tube 104 is disposed on the edge portion of a chassis 102. A light guide member 106 is disposed on the side of the cold cathode tube 104, and a diffusing sheet 108 is disposed over the upper face of the light guide member 106, thereby configuring the back light illuminant 100.
A reflecting portion 116, which is made by a minute uneven structure or made by drawing a dot shape with a white ink for instance, is formed under the light guide member 106. Moreover, a liquid crystal panel 110 is laminated on the upper face of the diffusing member 108 of the back light illuminant 100, thereby configuring a liquid crystal display apparatus 112.
For the back light illuminant 100 of the edge light type, a light that has been irradiated from the cold cathode tube 104 by making the cold cathode tube 104 to be illuminant enters a side portion of the light guide member 106.
A light that has entered the light guide member 106 is diffused while repeating a reflection between the reflecting portion 116 that has been formed under the light guide member 106 and that is made by a minute uneven structure or made by drawing a dot shape with a white ink for instance, and an upper face 118 of the light guide member 106. The light is then uniformly guided upward from the upper face 118 of the light guide member 106.
By the above configuration, a light is uniformly diffused by the diffusing member 108, thereby reducing a nonuniformity in luminance of the liquid crystal panel 110.
However, a demand of enlarging a liquid crystal display has been increased in recent years, and such a back light illuminant 100 of the edge light type has a limitation in improving a luminance and a uniformity in the luminance.
Therefore, an adoption of a direct lighting type light is examined for a large size liquid crystal display.
However, in the case in which the above described cold cathode tube is used as a direct lighting type light, since the cold cathode tube is comparatively large, a thickness of a liquid crystal display is enlarged. In addition, there are problems that color reproducibility and a response of the cold cathode tube is not satisfactory, and that an after-image phenomenon occurs.
In recent years, a luminous efficiency of a luminous device has been extremely improved, and an application of the luminous device to an illumination is being progressed. In particular, in the case in which there is used a light emitting diode (hereafter referred to as an LED) as a back light illuminant (planar light source) for a liquid crystal display, an excellent color reproducibility and a high speed response can be implemented and it is expected that a high quality image is achieved.
Therefore, conventionally, there has been proposed a back light illuminant of a direct lighting type in which a plurality of LEDs is disposed at a constant pitch below a liquid crystal panel.
As such a back light illuminant of a direct lighting type, an illuminant with a configuration shown in FIG. 25 is proposed.
More specifically, for a back light illuminant 200 of the direct lighting type, a plurality of LED lamps 206 is disposed at a constant pitch in an array pattern on the bottom face 204 of a chassis 202.
A diffusing member 208 is disposed over the upper face of the chassis 202 apart at a constant distance from the LED lamps 206, and a prism sheet 210 is disposed over the upper face of the diffusing member 208, thereby configuring the back light illuminant 200.
A reflecting portion 214 made of a reflecting sheet or the like is formed on the bottom face 204 and a side face 212 of a chassis 202.
For the back light illuminant 200 of a direct lighting type that is configured as described above, in the case in which a light is generated from the LED lamps 206, the emitted light travels directly toward the diffusing sheet 208. In addition, the emitted light is also reflected by the reflecting portion 214 on the bottom face 204 and a side face 212 of a chassis 202, and travels toward the diffusing sheet 208.
The light that has entered the diffusing sheet 208 is then diffused in the diffusing sheet 208, and is inclined in a vertical direction by passing through the prism sheet 210 on the upper face of the diffusing sheet 208. The light then enters a liquid crystal panel (not shown) disposed over the upper face of the prism sheet 210.
Moreover, lights emitted from the LED lamps 206 are mixed in a space between the LED lamps and the diffusing sheet 208. The mixing is then improved by a diffusion in the diffusing sheet 208, thereby implementing a uniform luminance and a uniform chromaticity.
Moreover, in general, a luminance at the section directly over the LED lamps 206 is higher than that of other sections. Therefore, a uniformity in a luminance can be further improved by increasing a diffusability of the diffusing sheet 208 at the section directly over the LED lamps 206.
For the conventional the back light illuminant 200 of a direct lighting type, the diffusing sheet 208 is disposed and the diffusing sheet 208 is apart from the LED lamps 206 in order to uniform a luminance and a chromaticity as described above. However, even in such a case, the above means is insufficient to solve a problem that a luminance at the section directly over the LED lamps 206 becomes higher.
Recently, a color mixture is carried out by using LED lamps of a plurality of colors (RGB) composed of LEDs of three primary colors of red, green, and blue in particular (without using a monochromatic LED). In such a case, a color mixture is insufficient and an unevenness of colors may be found in some cases.
Accordingly, to decrease a nonuniformity in luminance and an unevenness of colors, a diffusability of the diffusing sheet 208 at the section directly over the LED lamps 206 is further increased as described above.
In addition, in Patent Document 1 (Japanese Laid-Open Patent Publication No. 2001-42782), a so-called lighting curtain such as a gray printing layer with a light semi-permeability is disposed directly over the LED lamps in order to reduce a luminance at the section directly over the LED lamps in some cases.
However, the above means cause a utilization efficiency of a light to be lowered.
Moreover, in the case in which the diffusing sheet 208 is made further apart from the LED lamps 206, a nonuniformity in luminance and an unevenness of colors can be decreased. However, this method causes a thickness of a back light to be enlarged, and is not preferable for a flat panel display.
Consequently, Patent Document 2 (Japanese Patent Publication No. 1998-82915) proposes a planar light source device 300 as shown in FIG. 26.
More specifically, for the planar light source device 300, a light guide member 306 is laminated on the upper face of a luminous device mounting substrate 308 on which an LED lamp 302 has been mounted. A concave for LED lamp housing 304 is formed in the light guide member 306 at the position corresponding to the LED lamp 302 in such a manner that a width of the concave is narrower at a deeper section from the surface of the light guide member.
Moreover, a reflecting portion 312 made of a reflecting sheet or the like is formed on the bottom face 310 of the light guide member 306 except for the section corresponding to the concave for LED lamp housing 304.
By the above configuration, as shown in FIG. 26, a light B1 that has been emitted from the LED lamp 302 is diffused while repeating a reflection between an upper face 314 of the light guide member 306 and the reflecting portion 312 formed on the bottom face 310 of the light guide member 306 as shown by an arrow B2, and is uniformly guided upward from the upper face 314 of the light guide member 306.
As a result, a light is uniformly diffused by a diffusing sheet (not shown) formed on the upper face of the light guide member 306, thereby preventing a nonuniformity in luminance from occurring and implementing a uniform luminance distribution at a light emitting plane of the light guide member 306.
Consequently, the planar light source device 300 disclosed in Patent Document 2 is thinner than conventional apparatuses, has little unevenness of colors, and is capable of improving a luminance.    [Patent document 1] Japanese Laid-Open Patent Publication No. 2001-42782    [Patent document 2] Japanese Patent Publication No. 1998-82915